The phagocytic neutralization of pathogens plays a central role in host protection against, and recovery from infection. The proposed project aims to expose the major mechanical determinants of phagocytosis by firmly integrating single-cell experiments with advanced theoretical models of "virtual immune cells". This interdisciplinary effort ties closely into the long-term objective of establishing a solid quantitative understanding of autonomous cell motility and its role in the innate immune response. An integrative experimental/theoretical approach will first be used to establish a baseline of key models of phagocytosis (Aim 1) and of different phagocytic pathways (Aim 2). It will then be applied to genetically altered model systems in order to elucidate the mechanical roles of major molecular components for normal phagocytic function (Aim 3). The method's relevance as a valuable single-cell assay in studies of the innate immune function will be validated by examining the phagocytosis of infectious pathogens (Aim 4). The experimental configuration most suitable for close integration with theoretical models consists of an initially spherical cell that engulfs a spherical bead. Single-cell phagocytosis of spherical targets will be monitored using a custom-built videomicroscopy/micropipette-manipulation setup. Data analysis will provide the time courses of cellular morphology, cortical tension, and bead movement for each experiment. These quantitative measurements will serve as standards for the validation of finite-element computer models that are based on physically realistic and biologically plausible rules. The models'success in reproducing the observations will place strong constraints on the forces at play in phagocytosis. The changes in parameter values that are required to accommodate genetically altered or diseased states will noninvasively expose the impact of the affected nanoscale structures on molecular motor activity and cytoskeletal properties. The focus on a standardized single cell/single target configuration that is highly reproducible and simple enough to be quantitatively analyzed presents a unique viewpoint on the phagocytic phenotype. The integration of experiment and theory reveals in detail how the immune phagocytic response fails or succeeds depending on the nature of both phagocyte and pathogen. This is a determining element for the recovery from infectious challenges in human health.